W-staged flame boiler for multi-stage combustion with multi-ejection and its  method thereof

ABSTRACT

A method for a flame boiler with multi-stage combustion with multi-ejection, includes the steps of ejecting inner and outer secondary air flows with speed of 35-65 m/s to guide a fuel-rich pulverized coal flow with speed of 10-20 m/s into a lower chamber to provide first and second combustion stages, ejecting lower secondary air flows with speed of 35-65 m/s into the lower chamber to further guide the pulverized coal so as to provide a third combustion stage. The system includes a lower chamber, an upper chamber, a combustion chamber, fuel-rich pulverized coal flow nozzles, fuel-lean pulverized coal flow nozzles respectively provided at the front and rear boiler arches, and lower secondary air nozzles provided at the front and rear water cooled walls. The combustion of the pulverized coal flow with W-shaped flowing path within the boiler is adapted to reduce NO x  emission and minimize the content of combustible substance in ash.

BACKGROUND OF THE PRESENT INVENTION

1. Field of Invention

The present invention relates to a method and apparatus for multi-stage combustion, more particularly to a W-shaped flame boiler for multi-stage combustion with multi-ejection and its method thereof.

2. Description of Related Arts

W-shaped flame boilers are one type of flame boilers especially designed for burning anthracites and lean coals. However, the W-shaped flame boilers have several major drawbacks during combustion operation. The NO_(x) emission of the W-shaped flame boilers is relatively high that the amount of NO_(x) is about 1600˜1800 mg/m³. The content of ash from the coal contains relatively high combustible substance. The slag is critically accumulated at the front and rear water cooling walls of the lower combustion chamber. The ignition of pulverized coal air flow is relatively sluggish and the combustion flame is relatively unstable.

FIGS. 3 and 4 illustrate the sectional view of the flow in the conventional combustion chamber and the burner nozzle arrangement of the boiler respectively. The above mentioned drawbacks are analyzed according to the structure of the boiler showed in the drawings. The reasons for the high NO emission are discussed as follows: Firstly, the fuel-rich pulverized coal flow nozzles 10 and the secondary air nozzles 20 are positioned in an alternating manner and closely to each other. The speed of secondary air 23 is higher than the speed of the fuel-rich pulverized coal flows 5 that the fuel-rich pulverized coal flows 5 will mix with the secondary air 23 when the secondary air 23 exits the secondary air nozzles 20. The speed of the fuel-rich pulverized coal flows 5 will be increased corresponding to the speed of the secondary air 23 so that the fuel-rich pulverized coal flows 5 will downstream with the secondary air 23. In other words, the fuel-rich pulverized coal flow 5 is an oxygen rich flow during the operation of the boiler so that large amount of NO_(x) will be produced. Secondly, the fuel-lean pulverized coal flow 7 is injected into the boiler through a nozzle which is adjacent to the center line 2-1 of the combustion chamber. Since the momentum of the fuel-lean pulverized coal flow 7 is relatively small, the fuel-lean pulverized coal flow 7 is redirected by the high-temperature fuel gas at the recirculation zone 22 to mix with the fuel-rich pulverized coal flow 5. Therefore, the expected result of reduction of NO production by mixing combustion of fuel-rich pulverized coal flows and fuel-lean pulverized coal flows cannot be achieved (the theoretical method of NO_(x) reduction is that the fuel-rich pulverized coal flow is mixed to form a high percentage of pulverized coal and low percentage of air during combustion, such that the fuel-rich pulverized coal flows with lean oxygen environment is combusted at the early combustion stage to minimize the production of NO_(x)). content of ash from the coal contains relatively high combustible substance

The main reason for the high content of combustible substance in ash is that the lower secondary air 9 is blown horizontally into the combustion chamber to block the downstream fuel-rich pulverized coal flows 5 so that the downstream fuel-rich pulverized coal flows 5 cannot be flowed deeper into the lower chamber 1. In other words, the travel route of the particles of the fuel in the lower chamber 1 is limited and the retention time is thus reduced. In addition, late ignition of the fuel and the unstable flame are also important factors to influence the content of combustible substance in the ash. Accordingly, the arrangement of the burner nozzles on the boiler arch has several drawbacks. (1) The fuel-rich pulverized coal flow nozzles 10 are provided adjacent to the front water cooled walls 2-2 or the rear water cooled wall 2-3 at a position relatively far away from the center line 2-1 of combustion chamber. However, the further the distance is away from the center line 2-1 of combustion chamber, the temperature of the flue gas is lower. Thus it is not beneficial for ignition because the temperature of the flue gas which is used for heating the fuel-rich pulverized coal flow is relatively low. (2) Each fuel-rich pulverized coal flow nozzle 10 has an elongated slot structure so that the effective heating area for the fuel-rich pulverized coal flow to heat exchange with the high-temperature flue gas is relatively small. Thus, the ignition of the pulverized coal flow and the stability of the flame are influenced. (3) The upper edges of the fuel-rich pulverized coal flow nozzles 10 are not aligned at the same level with the upper edges of the secondary air nozzles 20 so that there is an area defined between the upper edge of each fuel-rich pulverized coal flow nozzle 10 and the corresponding protruding portions of the adjacent secondary air nozzles 20 at the two sides thereof. In other words, there is no gas injecting into the combustion chamber through the area so that the space under the area is vacant and thus the secondary air 23 is easy to spread into that area. Therefore, a special air membrane is formed between the fuel-rich pulverized coal flows 5 and the high-temperature flue gas adjacent to the center line 2-1 of the combustion chamber so that the mixture thereof is blocked. As a result, the ignition is delayed and the combustion is unstable. (4) Each fuel-lean pulverized coal flow 7 is injected from the boiler arch into the central zone of the combustion chamber so that the mixture of the fuel-rich pulverized coal flows 5 and the high-temperature flue gas adjacent to the center line 2-1 of the combustion chamber is blocked. The low-temperature fuel-lean pulverized coal flow 7 will cool down the high-temperature flue gas adjacent to the center line 2-1 of the combustion chamber so as to affect the ignition and stable combustion.

The reasons of slag being accumulated at the front and rear water cooling walls of the lower combustion chamber are mentioned as follows.

(1) the fuel-rich pulverized coal flows 5 are sidewardly injected into the lower chamber 1 between the front water cooled wall 2-2 and the rear water cooled wall 2-3, wherein there are no other flow at the gap among the fuel-rich pulverized coal flow nozzles 10, the front water cooled wall 2-2, and the rear water cooled wall 2-3 of the lower chamber 1. Therefore, when the secondary air 23 with the fuel-rich pulverized coal flows 5 moves downwardly, the fuel-rich pulverized coal flows 5 will spread out at the front water cooled wall 2-2 and the rear water cooled wall 2-3 of the lower chamber 1, so as to accumulate the slag at the front water cooled wall 2-2 and the rear water cooled wall 2-3. (2) The downstream fuel-rich pulverized coal flows 5 will be expanded when the temperature thereof increases. In addition, the fuel-rich pulverized coal flows 5 will travel sidewardly at the center of the combustion chamber because of the expansion of the fuel-rich pulverized coal flows 5. Therefore, the fuel-rich pulverized coal flows 5 will contact with the front water cooled wall 2-2 and the rear water cooled wall 2-3 so as to accumulate the slag thereat.

China Patent, cited as document 1, discloses “W-shaped flame boiler with offsetting downward secondary air” (Patent Number ZL200610010089.5; date of patent: Jun. 24, 2009; date of application: May 26, 2006. Another China Patent, cited as document 2, discloses “Slot-type W-shaped flame boiler for stable combustion and slag preventing” (date of publication: Feb. 18, 2009; Application Number CN200810137213.3; date of application: Sep. 27, 2008. Another China Patent, cited as document 3, discloses “W-shaped flame boiler with elongated secondary air nozzles” (date of publication: Mar. 10, 2010; application number CN200910309100.1; date of application: Oct. 30, 2009. The above three documents have made some modifications in view of the aforesaid problems, to some extent, the situation is improved but the problems are not totally perfectly solved.

SUMMARY OF THE PRESENT INVENTION

The invention is advantageous in that it provides a W-shaped flame boiler for multi-stage combustion with multi-ejection and its method thereof, which solves the above mentioned problems of high NO_(x) emission, high percentage of combustible substance in the ash, slag being accumulated at the front and rear water cooled walls of the lower combustion chamber, late ignition of the pulverized coal flow, and unstable combustion flame.

The word “ejection” is defined that when there are two different flows with different speeds, the high speed flow has a relative low static pressure while the low speed flow has a relative high static pressure. When two flows are parallelly and spacedly ejected into the combustion chamber, a static pressure difference is generated between the two flows. Therefore, the low speed flow will move towards the high velocity flow and will finally mix with high speed flow. Accordingly, the low speed flow is guided to move by the high speed flow, such that the travel route of the low speed flow will be prolonged.

According to the present invention, the foregoing and other objects and advantages are attained by providing a method for a flame boiler with multi-stage combustion with multi-ejection, wherein the method comprises the following steps. A plurality of fuel-rich pulverized coal flow nozzles, a plurality of inner secondary air nozzles, a plurality of fuel-lean pulverized coal flow nozzles, and a plurality of outer secondary air nozzles are orderly configured at a combustion chamber. In particular, the fuel-rich pulverized coal flow nozzles, the inner secondary air nozzles, the fuel-lean pulverized coal flow nozzles, and the outer secondary air nozzles are alignedly and orderly located between a center line of the combustion chamber and a front water cooled wall of the combustion chamber at a front boiler arch and between the center line of the combustion chamber to a rear water cooled wall of the combustion chamber at a rear boiler arch. Fuel-rich pulverized coal flows, inner secondary air flows, fuel-lean pulverized coal flows, outer secondary air flows are ejected into a lower chamber of the combustion chamber. In particular, the fuel-rich pulverized coal flows are ejected into the lower chamber through the fuel-rich pulverized coal flow nozzles respectively. The inner secondary air flows are ejected into the lower chamber through the inner secondary air nozzles respectively. The fuel-lean pulverized coal flows are ejected into the lower chamber through the fuel-lean pulverized coal flow nozzles respectively. The outer secondary air flows are ejected into the lower chamber through the outer secondary air nozzles respectively. The speed of the inner secondary air flow is about 35-65 m/s. The speed of the outer secondary air flow is about 35-65 m/s. The speed of the fuel-rich pulverized coal flow is about 10-20 m/s. The inner and outer secondary air flows are sequently ejected into the lower chamber to mix and guide with the fuel-rich pulverized coal flow in a down-streaming manner so as to provide a first combustion stage and a second combustion stage respectively. Lower secondary air flows are ejected into the lower chamber, wherein the speed of the lower second air flow is about 35-65 m/s. In particularly, a plurality of lower secondary air nozzles are provided at the front and rear water cooled wall of the lower chamber respectively, wherein the lower secondary air flows are ejected into the lower chamber through the lower secondary air nozzles respectively. The lower second air flows are ejected into the lower chamber to mix and guide with the fuel-rich pulverized coal flow in a down-streaming manner so as to further provide a third combustion stage. The lower secondary air nozzles are inclinedly extended from the front and rear water cooled wall, wherein an inclination angle α of each of the lower secondary air nozzles is about 25°-45° with respect to the horizontal level which is perpendicular to the center line of the combustion chamber. Accordingly, the fuel-rich pulverized coal flow nozzles, the fuel-lean pulverized coal flow nozzles, the lower secondary air nozzles, the inner secondary air nozzles and the outer secondary air nozzles all have rectangular cross section or round cross section. The fuel-rich pulverized coal flow nozzle with rectangular cross section has a length-width ratio of 4˜5:1.

Additional advantages and features of the invention will become apparent from the description which follows, and may be realized by means of the instrumentalities and combinations particular point out in the appended claims.

In accordance with another aspect of the invention, the present invention provides a W-shaped flame boiler for multi-stage combustion with multi-ejection is illustrated, wherein the W-shaped flame boiler comprises a lower chamber, an upper chamber positioned below the lower chamber, and a combustion chamber formed by two boiler arches. The boiler further comprises a plurality of fuel-rich pulverized coal flow nozzles, a plurality of fuel-lean pulverized coal flow nozzles, and a plurality of lower secondary air nozzles. Accordingly, the two boiler arches are front boiler arch and rear boiler arch respectively. The W-shaped flame boiler further comprises a plurality of inner secondary air nozzles and a plurality of outer secondary air nozzles, wherein the inner and outer secondary air nozzles generate two sequent air flows. The fuel-rich pulverized coal flow nozzles, the inner secondary air nozzles, the fuel-lean pulverized coal flow nozzles, and the outer secondary air nozzles are alignedly and orderly located between a center line of the combustion chamber and a front water cooled wall of the combustion chamber at the front boiler arch and between the center line of the combustion chamber to a rear water cooled wall of the combustion chamber at the rear boiler arch. A plurality of lower secondary air nozzles are provided at the front and rear water cooled wall of the lower chamber respectively. The lower secondary air nozzles are inclinedly extended from the front and rear water cooled wall, wherein an inclination angle of each of the lower secondary air nozzles is about 25°-45° with respect to the horizontal level which is perpendicular to the center line of the combustion chamber. The fuel-rich pulverized coal flow nozzles are grouped to form a plurality of fuel-rich pulverized coal flow nozzle arrangements. Preferably, each fuel-rich pulverized coal flow nozzle arrangement has two fuel-rich pulverized coal flow nozzles positioned close to each other, wherein the fuel-rich pulverized coal flow nozzle arrangements are aligned at an in-line formation along the transverse direction of the combustion chamber and evenly spaced apart with each other. The fuel-lean pulverized coal flow nozzles are grouped to form a plurality of fuel-lean pulverized coal flow nozzle arrangements. Preferably, each fuel-lean pulverized coal flow nozzle arrangement has two fuel-lean pulverized coal flow nozzles positioned close to each other, wherein the fuel-lean pulverized coal flow nozzle arrangements are aligned at an in-line formation along the transverse direction of the combustion chamber and evenly spaced apart with each other. The inner secondary air nozzles are aligned at an in-line formation along the transverse direction of the combustion chamber and evenly spaced apart with each other. The outer secondary air nozzles are aligned at an in-line formation along the transverse direction of the combustion chamber and evenly spaced apart with each other. The fuel-rich pulverized coal flow nozzles, the fuel-lean pulverized coal flow nozzles, the lower secondary air nozzles, the inner secondary air nozzles and the outer secondary air nozzles are all communicating with the lower chamber. Accordingly, the fuel-rich pulverized coal flow nozzles, the fuel-lean pulverized coal flow nozzles, the lower secondary air nozzles, the inner secondary air nozzles and the outer secondary air nozzles all have rectangular cross section or round cross section. The fuel-rich pulverized coal flow nozzle with rectangular cross section has a length-width ratio of 4˜5:1.

The present invention has advantages, in comparison with the prior art, of reduction of NO_(x) emission and the content of combustible substance in ash, minimum of slag being accumulated at the front and rear water cooled walls of the lower chamber, early ignition and stable combustion. The following description will discuss in details.

Reduction of NO_(x) Emission:

(1) The fuel-rich pulverized coal flow nozzles 10, the inner secondary air nozzles 11, the fuel-lean pulverized coal flow nozzles 12, and the outer secondary air nozzles 13 are alignedly and orderly located between a center line 2-1 of the combustion chamber and a front water cooled wall 2-2 of the combustion chamber at a front boiler arch 3 and between the center line 2-1 of the combustion chamber to a rear water cooled wall 2-3 of the combustion chamber at a rear boiler arch 15. Fuel-rich pulverized coal flows 5, inner secondary air flows 6, fuel-lean pulverized coal flows 7, and outer secondary air flows 8 are ejected into a lower chamber 1 of the combustion chamber. The inner and outer secondary air flows 6, 7 with the speed about 35-65 m/s are sequently ejected into the lower chamber 1 to mix and guide with the fuel-rich pulverized coal flow 5 with the speed about 10-20 m/s in a down-streaming manner so as to provide a first combustion stage and a second combustion stage respectively. Since the fuel-rich pulverized coal flows 5 is prevented from being mixed the secondary air too early, the fuel-rich pulverized coal flows 5 are combusted in an oxygen-lean environment for prolonging the combustion time so as to reduce the NO_(x) production. In other words, the fuel-rich pulverized coal flows 5 are ejected to a predetermined depth by the inner secondary air flow 6 which is closely adjacent to the fuel-rich pulverized coal flows 5. Meanwhile, sufficient air is provided for the combustion of the pulverized coal flow. The downstream secondary air flows 8 are ejected into the lower chamber 1 adjacent to the front and rear water cooled walls 2-2, 2-3, that when the downstream secondary air flows 8 are ejected into the bottom portion of the lower chamber 1, the secondary air flows 8 will mix with the fuel-rich pulverized coal flows 5, the inner secondary air 6 and the fuel-lean pulverized coal flows 7. In other words, the pulverized coal flows will guide to flow into the bottom portion of the lower chamber 1 through the secondary air flows 8. (2) The inner secondary air 6 forms a partition between the fuel-rich pulverized coal flows 5 and the fuel-lean pulverized coal flows 7 for postponing the mixing process between the fuel-rich pulverized coal flows 5 and the fuel-lean pulverized coal flows 7, so as to separate the combustions of the fuel-rich pulverized coal flows 5 and the fuel-lean pulverized coal flows 7 and to reduce the NO_(x) production. (3) The lower secondary air flow 9 with a speed of 35-65 m/s is ejected into the lower chamber 1 through the lower secondary air nozzle 14, wherein an inclination angle α of each of the lower secondary air nozzles 14 is about 25°-45° with respect to the horizontal level which is perpendicular to the center line of the combustion chamber. The lower second air flows 9 are ejected at an predetermined ejection angle into the lower chamber 1 to mix and guide with the fuel-rich pulverized coal flow 5 in a down-streaming manner so as to further provide a third combustion stage. In addition, the lower secondary air flow 9 at the predetermined ejection angle will postpone the mixing process between the pulverized coal flows and the lower secondary air flow 9, so as to prolong the combustion time for the pulverized coal flows being combusted under the oxygen-lean environment and to reduce the NO_(x) production.

In other words, the fuel-rich pulverized coal flows 5 are separated from the secondary air in the boiler arch so that the fuel-rich pulverized coal flows 5 are guided to flow into the combustion chamber through the inner secondary air 6 and the outer secondary air 8, and then is further guided into the lower chamber through the lower secondary air 9. Therefore, the pulverized coal flows will have multi-stage combustion with multi-ejection that the pulverized coal flows will be combusted under an oxygen-lean environment for a relatively long combustion time so as to reduce the NO_(x) production. Therefore, the combustions of fuel-rich pulverized coal flows and fuel-lean pulverized coal flows are accomplished to dramatically reduce the NO_(x) emission.

Reduction of Content of Combustible Substance in Ash:

(1) The fuel-rich pulverized coal flows 5 are configured at a position adjacent to the center line 2-1 of the combustion chamber. Since the temperature of the central zone of the combustion chamber is relatively high, the fuel-rich pulverized coal flows 5 will easily mix with the high-temperature recirculation fuel gas to accomplish timely ignition and stable combustion. Therefore, the fuel will be combusted efficiently. (2) Each fuel-rich pulverized coal flow nozzle 10 has a rectangular shaped cross section with a length-width ratio of 4˜5:1 rather than the elongated slot shape in the prior art with a length-width ratio of 10˜12:1. The modified structure has several advantages of increasing the effective heating surface of the fuel-rich pulverized coal flows 5 for heat exchange with the high-temperature recirculation flue gas so that timely ignition and stable combustion is accomplished. The fuel is combusted efficiently. In addition, the attenuation of pulverized coal flows is delayed because the fuel-rich pulverized coal flows 5 are concentratively flowed along the transverse direction of the combustion chamber. Therefore, the travel route of the fuel-rich pulverized coal flows 5 is prolonged to ensure the fuel being combusted efficiently. (3) From the boiler arch, the fuel-rich pulverized coal flows 5 with a speed of 10-20 m/s are ejected and guided to downstream into the combustion chamber by the inner and outer secondary air flows 6 with the speed of 35˜65 m/s to provide the first combustion stage and second combustion stage respectively. Then, when the downstream pulverized coal flows reach the zone near the lower secondary air nozzle 14, the lower secondary air flow 9 with the speed of 35-65 m/s is ejected to further guide the downstream pulverized coal to the bottom portion of the lower chamber 1. Therefore, the downstream pulverized coal will be guided to flow deep into the lower chamber 1 to prolong the particles of the downstream pulverized coal being stayed in the combustion chamber so as to enable the fuel being combusted efficiently and the content of combustible substance in ash being reduced. In other words, the efficiency of the boiler is substantially increased.

Reduction of slag being acclimated at the front and rear water cooled walls of the lower chamber:

The fuel-rich pulverized coal flows 5 are guided to flow adjacent to the center line 2-1 of the combustion chamber, and the fuel-lean pulverized coal flows 7 are guided to flow adjacent to the front and rear water cooled walls 2-2, 2-3. The fuel-lean pulverized coal flows 7 are guided to flow between the inner secondary air flow 6 and the outer secondary air flow 8. The outer secondary air flow 8 not only successfully prevents the coal particles of the fuel-lean pulverized coal flows 7 and the fuel-rich pulverized coal flows 5 being contacted with the front and rear water cooled walls, but also reduces the temperature at the area near the front and rear water cooled walls. Therefore, slag being accumulated at the front and rear water cooled walls of the combustion chamber is effectively reduced.

Earlier ignition and stable combustion of the fuel-rich pulverized coal flows:

(1) The fuel-rich pulverized coal flow nozzles 10 are provided adjacent to the center line 2-1 of the combustion chamber. There is no secondary air flow or fuel-lean pulverized coal flow provided between the fuel-rich pulverized coal flows 5 and the center line 2-1 of the combustion chamber. The temperature of the fuel gas which is under the fuel-rich pulverized coal flows 5 is relatively high and the fuel-rich pulverized coal flows 5 are not diluted by any secondary air flow or fuel-lean pulverized coal flows before the combustion of the fuel-rich pulverized coal flows 5. Therefore, a high temperature zone with rich fuel is formed under the fuel-rich pulverized coal flows 5. Since the concentration of the pulverized coal is high, the starting ignition heat will be reduced and the ignition temperature is low. Therefore, earlier ignition and stable combustion of the fuel-rich pulverized coal flows are achieved. (2) Each fuel-rich pulverized coal flow nozzle 10 is has a rectangular shaped cross section with a length-width ratio of 4˜5:1 rather than the elongated slot shape in the prior art with a length-width ratio of 10˜12:1. The modified structure has several advantages of increasing the effective heating surface of the fuel-rich pulverized coal flows 5 for heat exchange with the high-temperature recirculation flue gas for timely ignition and stable and enhancing the fuel being combusted efficiently.

Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.

These and other objectives, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the fuel flow path of the W-shaped flame boiler for multi-stage combustion with multi-ejection according to a preferred embodiment of the present invention, wherein the fuel flow configuration is symmetric with respect to the center line 2-1 of the combustion chamber and the downstream direction of each flow is illustrated with arrows.

FIG. 2 illustrates the configuration of the nozzles according to the above preferred embodiment of the present invention.

FIG. 3 is a schematic view of the fuel flow path of the conventional W-shaped flame boiler, wherein the downstream direction of each flow is illustrated with arrows.

FIG. 4 illustrates the configuration of the nozzles of the conventional W-shaped flame boiler.

FIG. 5 illustrates the configuration of the nozzles of the conventional W-shaped flame boiler according to “Document 2”.

FIG. 6 illustrates the configuration of the nozzles of the conventional W-shaped flame boiler according to “Document 3”.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2 of the drawings, a method for multi-stage combustion with multi-ejection is illustrated, wherein the method comprises the following steps. A plurality of fuel-rich pulverized coal flow nozzles 10, a plurality of inner secondary air nozzles 11, a plurality of fuel-lean pulverized coal flow nozzles 12, and a plurality of outer secondary air nozzles 13 are orderly configured at a combustion chamber. In particular, the fuel-rich pulverized coal flow nozzles 10, the inner secondary air nozzles 11, the fuel-lean pulverized coal flow nozzles 12, and the outer secondary air nozzles 13 are alignedly and orderly located between a center line 2-1 of the combustion chamber and a front water cooled wall 2-2 of the combustion chamber at a front boiler arch 3 and between the center line 2-1 of the combustion chamber to a rear water cooled wall 2-3 of the combustion chamber at a rear boiler arch 15. Fuel-rich pulverized coal flows 5, inner secondary air flows 6, fuel-lean pulverized coal flows 7, and outer secondary air flows 8 are ejected into a lower chamber 1 of the combustion chamber. In particular, the fuel-rich pulverized coal flows 5 are ejected into the lower chamber 1 through the fuel-rich pulverized coal flow nozzles 10 respectively. The inner secondary air flows 6 are ejected into the lower chamber 1 through the inner secondary air nozzles 11 respectively. The fuel-lean pulverized coal flows 7 are ejected into the lower chamber 1 through the fuel-lean pulverized coal flow nozzles 12 respectively. The outer secondary air flows 8 are ejected into the lower chamber 1 through the outer secondary air nozzles 13 respectively. The speed of the inner secondary air flow 6 is about 35-65 m/s. The speed of the outer secondary air flow 7 is about 35-65 m/s. The speed of the fuel-rich pulverized coal flow 5 is about 10-20 m/s. The inner and outer secondary air flows 6, 7 are sequently ejected into the lower chamber 1 to mix and guide with the fuel-rich pulverized coal flow 5 in a down-streaming manner so as to provide a first combustion stage and a second combustion stage respectively. Lower secondary air flows 9 are ejected into the lower chamber 1, wherein the speed of the lower second air flow 9 is about 35-65 m/s. In particularly, a plurality of lower secondary air nozzles 14 are provided at the front and rear water cooled wall 2-2, 2-3 of the lower chamber 1 respectively, wherein the lower secondary air flows 9 are ejected into the lower chamber 1 through the lower secondary air nozzles 14 respectively. The lower second air flows 9 are ejected into the lower chamber 1 to mix and guide with the fuel-rich pulverized coal flow 5 in a down-streaming manner so as to further provide a third combustion stage. The lower secondary air nozzles 14 are inclinedly extended from the front and rear water cooled wall 2-2, 2-3, wherein an inclination angle α of each of the lower secondary air nozzles 14 is about 25°-45° with respect to the horizontal level which is perpendicular to the center line of the combustion chamber. Accordingly, the fuel-rich pulverized coal flow nozzles 10, the fuel-lean pulverized coal flow nozzles 12, the lower secondary air nozzles 14, the inner secondary air nozzles 11 and the outer secondary air nozzles 13 all have rectangular cross section or round cross section. The fuel-rich pulverized coal flow nozzle 10 with rectangular cross section has a length-width ratio of 4˜5:1. For a pulverized coal boiler with a large capacity (such as 600 MW), the depth of the lower chamber 1 is about 16 m. The ejection of the inner and outer second air flows 6, 8, and the ejection of the lower second air flows 14 will ensure the flow of downstream pulverized coal being guided to the bottom of the lower chamber 1 so as to enhance the combustion sufficiency.

Preferably, the inclination angle α of each of the lower secondary air nozzles 14 is 45°. Accordingly, when the inclination angle α of each of the lower secondary air nozzles 14 is too large, the lower second air flow 9 ejecting from the respective lower secondary air nozzle 14 will be guided to flow deeper into the lower chamber 1, such that the downstream pulverized coal flows will be guided too deep at the lower chamber 1 to flush at the cold ash funnel 4 so as to accumulate the slag at the cold ash funnel 4. Configuring the inclination angle α of the lower secondary air nozzle 14 at 45°, the direction of the lower second air flow 9 will be perfectly guided into the lower chamber 1 to ensure of the downstream pulverized coal flows being flowed deep enough into the lower chamber 1 and to prevent the slag being accumulated at the cold ash funnel 4.

Referring to FIGS. 1 and 2 of the drawings, the W-shaped flame boiler for multi-stage combustion with multi-ejection is illustrated, wherein the W-shaped flame boiler comprises a lower chamber 1, an upper chamber 2 positioned below the lower chamber 1, and a combustion chamber formed by two boiler arches. The boiler further comprises a plurality of fuel-rich pulverized coal flow nozzles 10, a plurality of fuel-lean pulverized coal flow nozzles 12, and a plurality of lower secondary air nozzles 14. Accordingly, the two boiler arches are front boiler arch 3 and rear boiler arch 15 respectively. The W-shaped flame boiler further comprises a plurality of inner secondary air nozzles 11 and a plurality of outer secondary air nozzles 13, wherein the inner and outer secondary air nozzles 11, 13 generate two sequent air flows. The fuel-rich pulverized coal flow nozzles 10, the inner secondary air nozzles 11, the fuel-lean pulverized coal flow nozzles 12, and the outer secondary air nozzles 13 are alignedly and orderly located between a center line 2-1 of the combustion chamber and a front water cooled wall 2-2 of the combustion chamber at the front boiler arch 3 and between the center line 2-1 of the combustion chamber to a rear water cooled wall 2-3 of the combustion chamber at the rear boiler arch 15. A plurality of lower secondary air nozzles 14 are provided at the front and rear water cooled wall 2-2, 2-3 of the lower chamber 1 respectively. The lower secondary air nozzles 14 are inclinedly extended from the front and rear water cooled wall 2-2, 2-3, wherein an inclination angle α of each of the lower secondary air nozzles 14 is about 25°-45° with respect to the horizontal level which is perpendicular to the center line of the combustion chamber. The fuel-rich pulverized coal flow nozzles 10 are grouped to form a plurality of fuel-rich pulverized coal flow nozzle arrangements 16. Preferably, each fuel-rich pulverized coal flow nozzle arrangement 16 has two fuel-rich pulverized coal flow nozzles 10 positioned close to each other, wherein the fuel-rich pulverized coal flow nozzle arrangements 16 are aligned at an in-line formation along the transverse direction of the combustion chamber and evenly spaced apart with each other. The fuel-lean pulverized coal flow nozzles 12 are grouped to form a plurality of fuel-lean pulverized coal flow nozzle arrangements 17. Preferably, each fuel-lean pulverized coal flow nozzle arrangement 17 has two fuel-lean pulverized coal flow nozzles 12 positioned close to each other, wherein the fuel-lean pulverized coal flow nozzle arrangements 17 are aligned at an in-line formation along the transverse direction of the combustion chamber and evenly spaced apart with each other. The inner secondary air nozzles 11 are aligned at an in-line formation along the transverse direction of the combustion chamber and evenly spaced apart with each other. The outer secondary air nozzles 13 are aligned at an in-line formation along the transverse direction of the combustion chamber and evenly spaced apart with each other. The fuel-rich pulverized coal flow nozzles 10, the fuel-lean pulverized coal flow nozzles 12, the lower secondary air nozzles 14, the inner secondary air nozzles 11 and the outer secondary air nozzles 13 are all communicating with the lower chamber 1. Accordingly, the fuel-rich pulverized coal flow nozzles 10, the fuel-lean pulverized coal flow nozzles 12, the lower secondary air nozzles 14, the inner secondary air nozzles 11 and the outer secondary air nozzles 13 all have rectangular cross section or round cross section. The fuel-rich pulverized coal flow nozzle 10 with rectangular cross section has a length-width ratio of 4-5:1. For a pulverized coal boiler with a large capacity (such as 600 MW), the depth of the lower chamber 1 is about 16 m. The ejection of the inner and outer second air flows 6, 8, and the ejection of the lower second air flows 14 will ensure the flow of downstream pulverized coal being guided to the bottom of the lower chamber 1 so as to enhance the combustion sufficiency.

It is appreciated that an alternative mode of the fuel-rich pulverized coal flow nozzle 10 is illustrated in FIG. 2, wherein the fuel-rich pulverized coal flow nozzle 10 has a round shaped cross section. Accordingly, the total cross sectional area of the fuel-rich pulverized coal flow nozzle 10 with the round cross section is the same as the total cross sectional area of the fuel-rich pulverized coal flow nozzle 10 with the rectangular cross section. The total cross sectional area of the fuel-lean pulverized coal flow nozzle 12 with the round cross section is the same as the total cross sectional area of the fuel-lean pulverized coal flow nozzle 12 with the rectangular cross section. The total cross sectional area of the lower secondary air nozzle 14 with the round cross section is the same as the total cross sectional area of the fuel lower secondary air nozzle 14 with the rectangular cross section. The total cross sectional area of the inner secondary air nozzle 11 with the round cross section is the same as the total cross sectional area of the inner secondary air nozzle 11 with the rectangular cross section. The total cross sectional area of the outer secondary air nozzle 13 with the round cross section is the same as the total cross sectional area of the outer secondary air nozzle 13 with the rectangular cross section. It is worth mentioning that FIG. 2 illustrates the fuel-rich pulverized coal flow nozzles 10, the inner secondary air nozzles 11, the fuel-lean pulverized coal flow nozzles 12, and the outer secondary air nozzles 13 are formed with rectangular cross section. In other words, the circular cross sectional fuel-rich pulverized coal flow nozzles 10 will generate the fuel-rich pulverized coal flows 5 with circular cross section into the combustion chamber. The circular cross sectional fuel-lean pulverized coal flow nozzles 12 will generate the fuel-lean pulverized coal flows 7 with circular cross section into the combustion chamber. The circular cross sectional inner secondary air nozzles 11 will generate the inner secondary air flows 6 with circular cross section into the combustion chamber. The circular cross sectional outer secondary air nozzles 13 will generate the outer secondary air flows 8 with circular cross section into the combustion chamber. The circular cross sectional lower secondary air nozzles 14 will generate the lower secondary air flows 9 with circular cross section into the combustion chamber, wherein the lower secondary air flows 9 with circular cross section is stable and is strong enough to guide the fuel-rich pulverized coal flows 5 deep into the lower chamber 1.

Referring to FIG. 1 of the drawing, the fuel-rich pulverized coal flow nozzles 10 at the front boiler arch 3 are symmetrically aligned with the fuel-rich pulverized coal flow nozzles 10 at the rear boiler arch 15 along the center line 2-1 of the combustion chamber. The inner secondary air nozzles 11 at the front boiler arch 3 are symmetrically aligned with the inner secondary air nozzles 11 at the rear boiler arch 15 along the center line 2-1 of the combustion chamber. The fuel-lean pulverized coal flow nozzles 12 at the front boiler arch 3 are symmetrically aligned with the fuel-lean pulverized coal flow nozzles 12 at the rear boiler arch 15 along the center line 2-1 of the combustion chamber. The outer secondary air nozzles 13 at the front boiler arch 3 are symmetrically aligned with the outer secondary air nozzles 13 at the rear boiler arch 15 along the center line 2-1 of the combustion chamber.

The fuel-rich pulverized coal flows 5, the fuel-lean pulverized coal flows 7, the inner secondary air flows 6, the outer secondary air flows 8 and the lower secondary air flows 9 are all symmetrically ejected into the combustion chamber along the center line 2-1 of the combustion chamber. Therefore, all the downstream flows are guided to move under the front and rear boiler arch 3, 15 in the lower chamber 1 with a W-shaped path with respect to the center line 2-1 of the combustion chamber. In other words, the downstream flows are evenly combusted in the lower chamber 1 in a symmetrical configuration below the front and rear boiler arch 3, 15 with respect to the center line 2-1 of the combustion chamber.

A cold modularization test platform is provided for a 300 MW W-shaped flame boiler for comparing the conventional boiler and the three modifications of the burner nozzles of the boiler in the prior arts (i.e. “document 1”, “document 2” and “document 3”, with the configuration for multi-stage combustion with multi-ejection of the present invention to measure the depth of the downstream fuel-rich pulverized coal flows with cold modularization tests. The depth of the downstream fuel-rich pulverized coal flow is defined at the vertical distance L₁ between the direction turning point of the fuel-rich pulverized coal flow and the center of the fuel-rich pulverized coal flow nozzle, as shown in FIG. 1. The depths of the downstream fuel-rich pulverized coal flows are 7.5 m, 9.5 m, 9.1 m and 8.8 m according to the conventional boiler (as introduced in the Background), “document 1”, “document 2” and “document 3” respectively.

Accordingly, when the boiler employs the present invention for multi-stage combustion with multi-ejection, the distance h₁ from the mixing point of the fuel-rich pulverized coal flow 5 and the inner secondary air flow 6 to the opening of the fuel-rich pulverized coal flow nozzle 10 is 1.8 m. The distance h₂ from mixing point of the fuel-rich pulverized coal flow 5 and fuel-lean pulverized coal flow 7 to the opening of the fuel-rich pulverized coal flow nozzle 10 is 3.0 m. The distance h₃ from mixing point of the fuel-rich pulverized coal flow 5 and the outer secondary air flow 8 to the opening of the fuel-rich pulverized coal flow nozzle 10 is 5.0 m. In other words, the fuel-rich pulverized coal flow 5 with the inner secondary air flow 6, the outer secondary air 8 and the fuel-lean pulverized coal flow 7 are sequently mixed stage by stage. The depth of the downstream fuel-rich pulverized coal flow 5 is substantially increased to 12.5 m. The thermal stimulation results for the conventional boiler and the three modifications of the burner nozzles in the prior arts are that the NO emissions are 1882 mg/m³, 1817 mg/m³, 1723 mg/m³ and 1321 mg/m³ respectively. The contents of combustible substance in the ash are 11.2%, 8.3%, 5.4%, and 5.8% respectively. When the boiler employs the present invention for multi-stage combustion with multi-ejection, the NO_(x) emission will be reduced to 600 mg/m³ and the content of combustible substance in the ash will be reduced to 4.5%. Therefore, the NO_(x) emission is reduced diametrically while the operation of the boiler is cost effective. The thermal stimulation for the conventional boiler and the three modifications of the burner nozzles in the prior arts results also indicate that the average temperature of the flue gas near the front and rear water cooled walls are 792° C., 807° C., 703° C. and 628° C. respectively. The average oxygen concentration of the conventional boiler and the three modifications are 3.9%, 3.2%, 6.4% and 7.8% respectively. When the boiler employs the present invention for multi-stage combustion with multi-ejection, the average temperature of the flue gas at that area will be reduced to 620° C. and the average oxygen concentration will be increased to 8%. Therefore, since the front and rear water cooled walls 2-2, 2-3 of the combustion chamber provide a low-temperature and high oxygen concentration area, the slag accumulated at the front and rear water cooled walls 2-2, 2-3 of the combustion chamber will be minimized.

Accordingly, the operation principle of the present invention is that the inner and outer secondary air flows with relatively high speeds are sequently ejected to guide the downstream fuel-rich pulverized coal flow with relative low speed into the combustion chamber. Then, the lower secondary air flow is ejected at a predetermined angle to further guide the downstream pulverized coal flow into the lower chamber 1 for multi-stage combustion with multi-ejection, so as to reduce the production of NO_(x) during combustion. In addition, the fuel-rich pulverized coal flow is guided to flow close to the center line of the combustion chamber while the fuel-lean pulverized coal flow is guided to flow close to the front and rear water cooled walls of the combustion chamber. The configuration of the fuel-rich pulverized coal flow and the fuel-lean pulverized coal flow can further minimize the production of NO_(x) during combustion and enhance the stabilization of the combustion. The outer secondary air flow at the front and rear water cooled walls can also prevent the slag being accumulated thereat.

One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting.

It will thus be seen that the objects of the present invention have been fully and effectively accomplished. It embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims. 

1. A method for multi-stage combustion with multi-ejection by a boiler, comprising the steps of: orderly configuring a plurality of fuel-rich pulverized coal flow nozzles 10, a plurality of inner secondary air nozzles 11, a plurality of fuel-lean pulverized coal flow nozzles 12, and a plurality of outer secondary air nozzles 13 at a combustion chamber, wherein said fuel-rich pulverized coal flow nozzles 10, said inner secondary air nozzles 11, said fuel-lean pulverized coal flow nozzles 12, and said outer secondary air nozzles 13 are alignedly and orderly located between a center line 2-1 of said combustion chamber and a front water cooled wall 2-2 of said combustion chamber at a front boiler arch 3 and between said center line 2-1 of said combustion chamber to a rear water cooled wall 2-3 of said combustion chamber at a rear boiler arch; ejecting fuel-rich pulverized coal flows 5 into said lower chamber 1 through said fuel-rich pulverized coal flow nozzles 10 respectively, ejecting inner secondary air flows 6 into said lower chamber 1 through said inner secondary air nozzles 11 respectively, ejecting fuel-lean pulverized coal flows 7 into said lower chamber 1 through said fuel-lean pulverized coal flow nozzles 12 respectively, and ejecting outer secondary air flows 8 into said lower chamber 1 through said outer secondary air nozzles 13 respectively, wherein a speed of said inner secondary air flow 6 is about 35-65 m/s, a speed of said outer secondary air flow 7 is about 35-65 m/s, a speed of said fuel-rich pulverized coal flow 5 is about 10-20 m/s, wherein said inner and outer secondary air flows 6, 7 are sequently ejected into said lower chamber 1 to mix and guide with said fuel-rich pulverized coal flow 5 in a down-streaming manner so as to provide a first combustion stage and a second combustion stage respectively; ejecting lower secondary air flows 9 into the lower chamber 1 via a plurality of lower secondary air nozzles 14, wherein a speed of said lower second air flow 9 is about 35-65 m/s, wherein said lower secondary air nozzles 14 are provided at said front and rear water cooled wall 2-2, 2-3 of said lower chamber 1 respectively to eject said lower secondary air flows 9 into the lower chamber 1 and to mix and guide with said fuel-rich pulverized coal flow 5 in a down-streaming manner so as to further provide a third combustion stage; wherein said lower secondary air nozzles 14 are inclinedly extended from said front and rear water cooled wall 2-2, 2-3, wherein an inclination angle α of each of said lower secondary air nozzles 14 is about 25°-45°, wherein said fuel-rich pulverized coal flow nozzles 10, said fuel-lean pulverized coal flow nozzles 12, said lower secondary air nozzles 14, said inner secondary air nozzles 11 and said outer secondary air nozzles 13 all have a cross section selected from the group consisting of rectangular cross section and round cross section, wherein said fuel-rich pulverized coal flow nozzle 10 with rectangular cross section has a length-width ratio of 4˜5:1.
 2. The method, as recited in claim 1, wherein said inclination angle α of each of said lower secondary air nozzles 14 is 45°.
 3. A W-shaped flame boiler for multi-stage combustion with multi-ejection, comprising a lower chamber 1, an upper chamber 2 positioned below said lower chamber 1, a combustion chamber formed by two boiler arches which are front boiler arch 3 and rear boiler arch 15 respectively, a plurality of fuel-rich pulverized coal flow nozzles 10, a plurality of fuel-lean pulverized coal flow nozzles 12, a plurality of lower secondary air nozzles 14, a plurality of inner secondary air nozzles 11, and a plurality of outer secondary air nozzles 13, wherein said inner and outer secondary air nozzles 11, 13 generate two sequent air flows, wherein said fuel-rich pulverized coal flow nozzles 10, said inner secondary air nozzles 11, said fuel-lean pulverized coal flow nozzles 12, and said outer secondary air nozzles 13 are alignedly and orderly located between a center line 2-1 of said combustion chamber and a front water cooled wall 2-2 of said combustion chamber at said front boiler arch 3 and between said center line 2-1 of said combustion chamber to a rear water cooled wall 2-3 of said combustion chamber at said rear boiler arch 15, wherein a plurality of lower secondary air nozzles 14 are provided at said front and rear water cooled wall 2-2, 2-3 of said lower chamber 1 respectively at a position that said lower secondary air nozzles 14 are inclinedly extended from said front and rear water cooled wall 2-2, 2-3, wherein an inclination angle α of each of said lower secondary air nozzles 14 is about 25°-45°, wherein said fuel-rich pulverized coal flow nozzles 10 are grouped to form a plurality of fuel-rich pulverized coal flow nozzle arrangements 16, each said fuel-rich pulverized coal flow nozzle arrangement 16 has two fuel-rich pulverized coal flow nozzles 10 positioned close to each other, wherein said fuel-rich pulverized coal flow nozzle arrangements 16 are aligned at an in-line formation along a transverse direction of said combustion chamber and evenly spaced apart with each other, wherein said fuel-lean pulverized coal flow nozzles 12 are grouped to form a plurality of fuel-lean pulverized coal flow nozzle arrangements 17, each said fuel-lean pulverized coal flow nozzle arrangement 17 has two fuel-lean pulverized coal flow nozzles 12 positioned close to each other, wherein said fuel-lean pulverized coal flow nozzle arrangements 17 are aligned at an in-line formation along said transverse direction of said combustion chamber and evenly spaced apart with each other, wherein said inner secondary air nozzles 11 are aligned at an in-line formation along said transverse direction of said combustion chamber and evenly spaced apart with each other, wherein said outer secondary air nozzles 13 are aligned at an in-line formation along said transverse direction of said combustion chamber and evenly spaced apart with each other, wherein said fuel-rich pulverized coal flow nozzles 10, said fuel-lean pulverized coal flow nozzles 12, said lower secondary air nozzles 14, said inner secondary air nozzles 11 and said outer secondary air nozzles 13 are all communicating with said lower chamber 1, wherein said fuel-rich pulverized coal flow nozzles 10, said fuel-lean pulverized coal flow nozzles 12, said lower secondary air nozzles 14, said inner secondary air nozzles 11 and said outer secondary air nozzles 13 all have a cross section selected from the group consisting of rectangular cross section and round cross section, wherein said fuel-rich pulverized coal flow nozzle 10 with rectangular cross section has a length-width ratio of 4˜5:1.
 4. The W-shaped flame boiler, as recited in claim 3, wherein a total cross sectional area of said fuel-rich pulverized coal flow nozzle 10 with said round cross section is the same as a total cross sectional area of said fuel-rich pulverized coal flow nozzle 10 with said rectangular cross section, wherein a total cross sectional area of said fuel-lean pulverized coal flow nozzle 12 with said round cross section is the same as a total cross sectional area of said fuel-lean pulverized coal flow nozzle 12 with said rectangular cross section, wherein a total cross sectional area of said lower secondary air nozzle 14 with said round cross section is the same as a total cross sectional area of said fuel lower secondary air nozzle 14 with said rectangular cross section, wherein a total cross sectional area of said inner secondary air nozzle 11 with said round cross section is the same as a total cross sectional area of said inner secondary air nozzle 11 with said rectangular cross section, wherein a total cross sectional area of said outer secondary air nozzle 13 with said round cross section is the same as a total cross sectional area of said outer secondary air nozzle 13 with said rectangular cross section.
 5. The W-shaped flame boiler, as in claim 3 or 4, wherein said fuel-rich pulverized coal flow nozzles 10 at said front boiler arch 3 are symmetrically aligned with said fuel-rich pulverized coal flow nozzles 10 at said rear boiler arch 15 along said center line 2-1 of said combustion chamber, wherein said inner secondary air nozzles 11 at said front boiler arch 3 are symmetrically aligned with said inner secondary air nozzles 11 at said rear boiler arch 15 along said center line 2-1 of said combustion chamber, wherein said fuel-lean pulverized coal flow nozzles 12 at said front boiler arch 3 are symmetrically aligned with said fuel-lean pulverized coal flow nozzles 12 at said rear boiler arch 15 along said center line 2-1 of said combustion chamber, wherein said outer secondary air nozzles 13 at said front boiler arch 3 are symmetrically aligned with said outer secondary air nozzles 13 at said rear boiler arch 15 along said center line 2-1 of said combustion chamber. 